Energy receiver, detection method, power transmission system, detection device, and energy transmitter

ABSTRACT

An energy receiver includes: a power receiver coil configured to wirelessly receive power transmitted from a power transmitter; a detection section configured to detect a foreign object; and a power storage section configured to supply power to the detection section during detection of the foreign object.

TECHNICAL FIELD

The present disclosure relates to a detector detecting presence of aconductor such as a metal, a power receiver, a power transmitter, anon-contact power transmission system, and a detection method. Inparticular, the present disclosure relates to an energy receiver, adetection method, a power transmission system, a detection device, andan energy transmitter.

BACKGROUND ART

In recent years, a non-contact power transmission system supplying powerby wireless, that is, without contact is actively developed. A magneticfield resonance method attracts attention as a method realizingnon-contact power transmission. The magnetic field resonance method usesmagnetic field coupling between a transmission-side coil and areception-side coil to perform power transmission. The magnetic fieldresonance method has characteristics that magnetic fluxes shared betweena power feed source and a power feed destination is reduced by activelyusing resonance phenomenon.

In a well-known electromagnetic induction method, the coupling degree ofthe power transmission side and the power reception side is distinctlyhigh, and power feeding with high efficiency is possible. However, sincea coupling factor need to be maintained high, power transmissionefficiency between a power transmission side coil and a power receptionside coil (hereinafter, referred to as “efficiency between coils”) islargely deteriorated when a distance between the power transmission sideand the power reception side is increased or when positional deviationoccurs. On the other hand, the magnetic field resonance method hascharacteristics that the efficiency between coils is not deteriorated,even if a coupling factor is small, if a quality factor is high. Inother words, there is an advantage that an axial alignment between thepower transmission side coil and the power reception side coil is notnecessary and degree of freedom in position and distance between coilsis high. The quality factor is an index indicating relationship betweenretention and loss of energy in a circuit having the power transmissionside coil or the power reception side coil (indicating intensity ofresonance of a resonance circuit).

One of the most important factors in the non-contact power transmissionsystem is measures against heat generation of a foreign metal. Whenpower feeding is performed without contact, if a metal exists betweenthe power transmission side and the power reception side, an eddycurrent occurs and thus the metal may generate heat, irrespective of theelectromagnetic induction method or the magnetic field resonance method.To suppress the heat generation, various methods of detecting a foreignmetal are proposed. For example, a method using an optical sensor or atemperature sensor is known. However, a detection method using a sensoris high in cost when feeding range is wide like the magnetic fieldresonance method. In addition, for example, if the used sensor is atemperature sensor, output results of the temperature sensor depend onheat conductivity therearound so that devices on the transmission sideand the reception side are limited in design.

Accordingly, a method of observing change in parameters (a current, avoltage, and the like) when a foreign metal exists between the powertransmission side and the power reception side and determining presenceof a foreign metal is proposed. In such a method, its cost is allowed tobe suppressed without design limitation. For example, in PatentLiterature 1, a method of detecting a foreign metal with use ofmodulation degree of parameters at communication between the powertransmission side and the power reception side is proposed. In PatentLiterature 2, a method of detecting a foreign metal with use of eddycurrent loss (detection of foreign substance by DC-DC efficiency) isproposed.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Application Unexamined Publication No.    2008-206231-   PTL 2: Japanese Patent Application Unexamined Publication No.    2001-275280

SUMMARY OF INVENTION

However, in the methods proposed in Patent Literatures 1 and 2,influence of a metal housing on the power reception side is notconsidered. In the case of charging to general mobile devices, any metal(metal housings, metallic parts, and the like) is likely to be used inthe mobile devices, and thus it is difficult to determine whether thechange of the parameters is caused by “influence of the metal housingand the like” or by “a contained foreign metal”. In Patent Literature 2as an example, it is difficult to determine whether the eddy currentloss is caused by a metal housing in a mobile device or by a foreignmetal existing between a power transmission side and a power receptionside. As described above, the methods proposed in Patent Literatures 1and 2 do not detect a foreign metal with high accuracy.

In addition, typically, a mobile device includes a battery for chargingpower received without contact and a control circuit appropriatelycontrolling the battery. However, when a detection circuit detecting aforeign metal is operated by using power charged in the battery in themobile device, the mobile device is necessary to control the detectioncircuit while appropriately controlling the battery, and thus loadrelated to the control is large.

Moreover, when the remaining battery charge is little, it is difficultfor the mobile device to detect a foreign metal existing between themobile device and the power transmission side. If detection of a foreignmetal is not performed, power transmission from the power transmissionside is not performed because safety is not ensured, and thus thebattery is not charged.

It is desirable to detect a foreign metal existing between a powertransmission side and a power reception side and to improve detectionaccuracy, without loading a system (control) on the power receptionside.

According to an embodiment of the disclosure, there is provided anenergy receiver including: a power receiver coil configured towirelessly receive power transmitted from a power transmitter; adetection section configured to detect a foreign object; and a powerstorage section configured to supply power to the detection sectionduring detection of the foreign object.

According to an embodiment of the disclosure, there is provided adetection method including: charging a power storage section using powerwirelessly received from a power receiver coil; detecting whether aforeign object is within a range of the power receiver coil using adetection section; and powering the detection section during detectionof the foreign object using the power storage section.

According to an embodiment of the disclosure, there is provided a powertransmission system including: a power transmitter configured towirelessly transmit power to a power receiver, wherein, the powertransmitter includes (i) a power transmission coil configured totransmit power to the power receiver, (ii) a power transmission sectionconfigured to supply an AC signal to the power transmission coil, and(iii) a power transmitter control section configured to control thesupply of the AC signal from the power transmission section in responseto a signal transmitted from the power receiver, and the power receiverincludes (i) a power receiver coil configured to wirelessly receivepower from the power transmitter, (ii) a detection section configured todetect a foreign object, (iii) a power storage section configured tostore the power received from the power transmitter, the power storagesection operable to supply the power received to the detection sectionduring detection of the foreign object, and (iv) a power receivercontrol section configured to operate the detection section anddetermine whether the foreign object is within a range of the powertransmission coil.

According to an embodiment of the disclosure, there is provided adetection device including: a power receiver coil configured towirelessly receive power transmitted from a power transmitter; adetection section configured to detect whether a foreign object iswithin a range of the power receiver coil; and a power storage sectionconfigured to supply power to the detection section during detection ofthe foreign object.

According to an embodiment of the disclosure, there is provided anenergy transmitter including: a power transmission coil configured towirelessly transmit power to a power receiver; a detection sectionconfigured to detect a foreign object; and a power storage sectionconfigured to supply power to the detection section during detection ofthe foreign object.

According to an embodiment of the disclosure, there is provided anenergy receiver including: a power receiver coil configured towirelessly receive power transmitted from a power transmitter; adetection section configured to detect a foreign object; and a controlsection configured to activate the detection section during suspensionof power transmission to the power receiver coil.

According to one embodiment of the disclosure, there is provided adetector including: a resonance circuit including a secondary-side coil;a detection section measuring a quality factor of the resonance circuit;a power storage section charging power, from power received through thesecondary-side coil from a primary-side coil, by an amount of powerconsumed during the quality factor measurement in the detection section;and a control section operating the detection section, during suspensionof power transmission from the primary-side coil, with use of the powercharged in the power storage section.

According to one embodiment of the disclosure, there is provided a powerreceiver including: a secondary-side coil; a resonance circuit includingthe secondary-side coil; a detection section measuring a quality factorof the resonance circuit; a power storage section charging power, frompower received through the secondary-side coil from a primary-side coil,by an amount of power consumed during the quality factor measurement inthe detection section; and a control section operating the detectionsection, during suspension of power transmission from the primary-sidecoil, with use of the power charged in the power storage section.

According to one embodiment of the disclosure, there is provided a powertransmitter including: a primary-side coil transmitting power to asecondary-side coil; a power transmission section supplying an AC signalto the primary-side coil; and a control section controlling the supplyof the AC signal from the power transmission section in response to asignal indicating an electromagnetic coupling state based on a qualityfactor of a power receiver, the signal being transmitted from the powerreceiver mounted with the secondary-side coil.

According to one embodiment of the disclosure, there is provided anon-contact power transmission system including: a power transmittertransmitting power by wireless; and a power receiver receiving the powertransmitted from the power transmitter. The power receiver includes: aresonance circuit including a secondary-side coil; a detection sectionmeasuring a quality factor of the resonance circuit; a power storagesection charging power, from power received through the secondary-sidecoil from a primary-side coil, by an amount of power consumed during thequality factor measurement in the detection section; and a first controlsection operating the detection section, during suspension of powertransmission from the primary-side coil, with use of the power chargedin the power storage section. The power transmitter includes: theprimary-side coil transmitting power to the secondary-side coil of thepower receiver; a power transmission section supplying an AC signal tothe primary-side coil; and a second control section controlling thesupply of the AC signal from the power transmission section in responseto a signal indicating an electromagnetic coupling state based on aquality factor of the power receiver, the signal being transmitted fromthe power receiver.

According to one embodiment of the disclosure, there is provided adetection method including: charging power, in a power storage sectionof a power receiver in a non-contact power transmission system, by anamount of power consumed during quality factor measurement in adetection section of the power receiver, from power received from aprimary-side coil of a power transmitter through a secondary-side coilof a resonance circuit, the resonance circuit being provided in thepower receiver; operating the detection section and acquiring a physicalamount necessary for determining a quality factor of the resonancecircuit, during suspension of power transmission from the primary-sidecoil, with use of the power charged in the power storage section; andcalculating the quality factor from the physical amount necessary fordetermining the quality factor, by the power receiver or the powertransmitter in the non-contact power transmission system.

According to the above-described example embodiments of the disclosure,even when power feeding is not performed from the power transmissionside to the power reception side, by using the power by an amount ofpower consumed during quality factor measurement stored in the powerstorage section and disconnecting a circuit for detecting a foreignmetal from a system on the power reception side, a foreign metalexisting between the power transmission side and the power receptionside is detectable. Moreover, the detection of a foreign metal isperformed by measuring the secondary-side quality factor while powerfeeding is not performed from the power transmission side to the powerreception side. Accordingly, the detection of a foreign metal is notaffected by power feeding, and detection accuracy is improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph illustrating an example of a frequency characteristicof a gain when a quality factor of a serial resonance circuit ischanged.

FIG. 2 is a graph illustrating a relationship between an S value (acoupling factorx a quality factor) and efficiency between coils.

FIGS. 3A to 3C are schematic diagrams explaining measurement conditionswhen a primary-side quality factor is measured with a position of ametal being changed.

FIG. 4 is a circuit diagram illustrating an outline of a powertransmitter used in a non-contact power transmission system according toa first embodiment of the disclosure.

FIG. 5 is a block diagram illustrating an internal configuration exampleof the power transmitter (on a primary side) according to the firstembodiment of the disclosure.

FIG. 6 is a block diagram illustrating an internal configuration exampleof a power receiver (on a secondary side) according to the firstembodiment of the disclosure.

FIG. 7 is a waveform diagram illustrating a state of a voltage drop atan input end of a first regulator by a capacitor charging.

FIG. 8 is a flowchart illustrating processes during power feeding of thenon-contact power transmission system according to the first embodimentof the disclosure.

FIG. 9 is a flowchart illustrating processes in the case where a qualityfactor reflecting frequency sweep is calculated on the primary side (thepower transmitter).

FIG. 10 is a timing chart of operations in the non-contact powertransmission system according to the first embodiment of the disclosure.

FIG. 11 is a graph plotting a plurality of frequencies and qualityfactors.

FIG. 12 is a flowchart illustrating processes in the case where aquality factor reflecting frequency sweep is calculated on the secondaryside (the power receiver).

FIG. 13 is a flowchart illustrating processes in the case where aquality factor is calculated on the primary side (the powertransmitter).

FIG. 14 is a flowchart illustrating processes in the case where aquality factor is calculated on the secondary side (the power receiver).

FIGS. 15A and 15B are circuit diagrams illustrating other examples of aresonance circuit used in the non-contact power transmission system.

FIG. 16 is a graph illustrating a frequency characteristic of impedancein a serial resonance circuit according to a second embodiment of thedisclosure.

FIG. 17 is a graph illustrating a frequency characteristic of impedancein a parallel resonance circuit according to the second embodiment ofthe disclosure.

FIG. 18 is a circuit diagram for calculating a quality factor with useof a ratio of an imaginary component to a real component of impedanceaccording to a third embodiment of the disclosure.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described below referringto the accompanying drawings. Descriptions will be given in thefollowing order. Note that the same numerals are used to designatecommon components in the drawings, and the overlapping description willbe appropriately omitted.

1. First Embodiment (first to third switch sections: example ofswitching circuit between during power feeding and during quality factormeasurement)2. Second Embodiment (arithmetic processing section: example ofcalculating quality factor by half bandwidth method)3. Third Embodiment (arithmetic processing section: example ofcalculating quality factor with use of ratio of real component andimaginary component of impedance)4. Others (various modifications)

1. First Embodiment Introduction Description

The inventors have studied detection of a foreign metal with use of achange in a power-reception side quality factor (a secondary side), inorder to solve the above-described issue. The foreign metal means aconductor such as a metal existing between a power transmission side (aprimary side) and the power reception side. The conductor described inthis specification includes a conductor in the broad sense, that is, asemiconductor.

The quality factor is an index indicating a relationship between energyretention and energy loss, and is generally used as a value indicating asharpness of a resonance peak (intensity of resonance) of a resonancecircuit. In a serial resonance circuit using a coil and a capacitor(also referred to as a condenser), the quality factor is generallyexpressed by an expression (1), where R is a resistance value of theserial resonance circuit, L is an inductance value, and C is acapacitance value.

$\begin{matrix}\left\lbrack {{Numerical}\mspace{14mu} {Expression}\mspace{14mu} 1} \right\rbrack & \; \\{Q = {\frac{1}{R}\sqrt{\frac{L}{C}}}} & (1)\end{matrix}$

FIG. 1 is a graph illustrating an example of frequency characteristicsof a gain with the quality factor of the serial resonance circuit beingchanged.

When the quality factor is changed between 5 and 100 as an example,sharpness of the peak in the frequency characteristics of the gain isincreased as the quality factor is increased. Moreover, it is known thatthe resistance value R and the inductance value L illustrated in theexpression (1) are changed by approach of a foreign metal or influenceof an eddy current generated in the foreign metal. Specifically, thequality factor and the resonance frequency of the resonance circuit arelargely changed by the influence of the foreign metal around the coil.

Next, power transmission efficiency between a primary-side coil and asecondary-side coil (efficiency between coils) in a non-contact powertransmission system in a magnetic field resonance method will bedescribed.

It is known that a maximum theoretical value η_(max) of the efficiencybetween coils is expressed by an expression (2).

$\begin{matrix}\left\lbrack {{Numerical}\mspace{14mu} {Expression}\mspace{14mu} 2} \right\rbrack & \; \\{\eta_{\max} = \frac{S^{2}}{\left( {1 + \sqrt{1 + S^{2}}} \right)^{2}}} & (2)\end{matrix}$

Herein, S and Q are expressed by the following expressions.

[Numerical Expression 3]

S=kQ  (3)

[Numerical Expression 4]

Q=√{square root over (Q₁Q₂)}  (4)

Q indicates a quality factor in the entire non-contact powertransmission system, Q₁ indicates a primary-side quality factor, and Q₂indicates a secondary-side quality factor. In other words, in themagnetic field resonance method, the efficiency between coils η_(max) istheoretically and uniquely determined from a coupling factor k, theprimary-side quality factor (Q₁), and the secondary-side quality factor(Q₂). The coupling factor k is a degree of magnetic coupling between theprimary-side coil and the secondary-side coil. The quality factors Q₁and Q₂ are quality factors in a resonance circuit without load.Accordingly, when the quality factors both on the power transmissionside and the power reception side are high even if the coupling factor kis low, power transmission is allowed to be performed with highefficiency.

A relationship between an S value (coupling factor×quality factor) andthe efficiency between coils η_(max) is illustrated in FIG. 2.

In the magnetic field resonance method, even if the coupling factor k islow, the primary-side quality factor and the secondary-side qualityfactor of the resonance circuit are made high to increase degree offreedom in arrangement of the primary-side coil and the secondary-sidecoil. As an example, the design is made on the assumption that thecoupling factor k between the primary-side coil and the secondary-sidecoil is equal to or smaller than 0.5, and the quality factor of one orboth of the primary-side coil and the secondary-side coil is equal to orlarger than 100. The same applies to second and third embodiments whichwill be described later.

In the magnetic field resonance method, a coil having a high qualityfactor to some extent is used for power feeding so that the degree offreedom in the arrangement of the primary-side coil and thesecondary-side coil is increased. Similarly to the typical resonancecircuit described above, however, the quality factor and the resonancefrequency are largely changed due to influence of a metal.

FIGS. 3A to 3C illustrate measurement conditions of primary-side qualityfactor measurement with various metal positions.

In the measurement, a spiral coil used as a primary-side coil 1 had asize of 150 mm (vertical)×190 mm (horizontal). The spiral coil wasobtained by winding a litz wire (wire diameter φ is 1.0 mm) which is atwisted conductive wire of a plurality of thin copper wires. A metalpiece 6 having a size of 50 mm (vertical)×60 mm (horizontal)×0.05 mm(thickness) was used on the secondary side in place of a metal housing.Two metal pieces 6 made of aluminum or stainless steel were prepared.The measurement was carried out on three cases, namely, (1) a case wherethe metal piece 6 was located on the center of the primary-side coil 1(FIG. 3A), (2) a case where the metal piece 6 was located at (moved to)a position shifted from the center in a horizontal direction (FIG. 3B),and (3) a case where the metal piece 6 was located on an end of theprimary-side coil 1 (FIG. 3C).

The measurement results of the primary-side quality factor depending onthe metal position are illustrated in Table 1.

TABLE 1 Kind of Metal Aluminum Stainless Steel Metal Position No metal(1) (2) (3) (1) (2) (3) Primary-Side 212.9 174.8 151.1 173.1 55.45 47.2189.33 Quality factor

It is confirmed from the measurement results illustrated in Table 1 thatthe primary-side quality factor is largely changed depending on theposition of the metal piece 6 viewed from the primary side and the metalmaterial. It is obvious from the above-described expressions (1) to (3)that the primary-side quality factor largely affects the efficiencybetween coils (eddy current loss). Therefore, it is found that variationof influence degree of a metal housing is dominant to the reduction ofthe efficiency between coils (increase of eddy current loss) rather thana small foreign metal, and detection of a small foreign metal isdifficult. In other words, the primary-side quality factor is largelychanged depending on the secondary side (in which the metal positionmounted in the housing is considered to be different). Therefore it isdifficult to determine whether the change in the quality factor iscaused by a mixed foreign substance or by influence of a metal housingon the secondary side.

On the other hand, as viewed from the secondary-side coil, a positionalrelationship between the secondary-side coil and the metal housing doesnot change at all, and there is a no correlation in a positionalrelationship between the primary-side coil and the secondary-side coil.Specifically, although the quality factor of the secondary-side coil isalso decreased by influence of the metal housing, if a large foreignmetal does not exist near the primary-side coil, the secondary-sidequality factor is constant irrespective of the positional relationshipand efficiency.

Typically, a mobile device such as a mobile phone and a digital stillcamera is assumed as the device on the power reception side. In such amobile device, for maintaining strength or performing main otherfunctions such as phone call or imaging, it is difficult to eliminatemetals from the device main body. However, since the main purpose of theprimary-side coil is possibly charging, there is a possibility that thedevice main body on the power transmission side has a configurationwithout influence of metals. In such a case, the secondary-side qualityfactor has a constant value, and is largely changed only by approach ofa foreign metal.

The change degree of the secondary-side quality factor caused by aforeign metal was measured, and the results are illustrated in Table 2.

TABLE 2 Ls Rs Quality Change Metal Position Value Value Factor AmountNone 61.93 581 80.3 0 Center 61.79 779 59.77 25.56663 Right 5 mm 61.84826 56.45 29.70112 Right 10 mm 62.46 1054 44.69 44.3462 Right 15 mm62.82 1071 44.21 44.94396 Bottom 5 mm 61.8 803 58 27.77086 Bottom 10 mm61.91 909 51.32 36.08966 Bottom 15 mm 62.41 1082 43.49 45.8406 Bottom 20mm 62.74 1015 46.61 41.95517 Lower Right 5 mm 61.89 869 53.7 33.12578Lower Right 10 mm 62.7 1111 42.5 47.07347

Table 2 illustrates the measured change amount of the secondary-sidequality factor when an iron piece having a size of 10 mm square and athickness of 1.0 mm is approached to a coil having an external size of40 mm×50 mm and an internal size of 20 mm×30 mm. An “Ls value” indicatesan inductance value of the coil, an “Rs value” indicates an effectiveresistance value of the resonance circuit at the frequency f, and a“change amount” indicates a change amount with reference to a qualityfactor without iron. Although the change amount of the quality factordepends on the position of the iron piece, the quality factor is changed(lowered) by at least 25% compared with a case without iron (when themetal piece is located at the center).

In this way, the change of the secondary-side quality factor is possiblyused for detection of a foreign metal. In other words, it is conceivablethat setting of a threshold with respect to the change amount of thequality factor enables detection of a foreign metal. However, asdescribed in “Summary of Invention”, when a quality factor is measuredwith use of power received from a power transmission side, there is adifficulty in which a quality factor is not precisely measured due to aninfluence of the power received from the power transmission side, forexample. To use the change of the quality factor for detection of aforeign metal, a measurement method needs to be devised. Hereinafter, amethod of measuring a quality factor according to the disclosure will bedescribed.

[Principle of Quality Factor Measurement]

The principle of a quality factor measurement is described referring toFIG. 4.

FIG. 4 is a circuit diagram illustrating an outline of a powertransmitter used in a non-contact power transmission system, accordingto a first embodiment of the disclosure. The circuit of a powertransmitter 10 illustrated in FIG. 4 is an example of a most basiccircuit configuration (in magnetic field coupling) illustrating themeasurement principle of the primary-side quality factor. Although acircuit including a serial resonance circuit is illustrated, variousembodiments of a detailed configuration are available as long as thecircuit has a function of a resonance circuit. The quality factormeasurement of the resonance circuit uses a method which is also used inmeasurement instruments (LCR meter). Incidentally, although the circuitillustrated in FIG. 4 is an example of a resonance circuit of the powertransmitter (on the primary side), the same measurement principleapplies to a resonance circuit of a power receiver (on the secondaryside).

For example, when a metal piece exists near a primary-side coil 15 ofthe power transmitter 10, lines of magnetic force pass through the metalpiece to generate an eddy current in the metal piece. As viewed from theprimary-side coil 15, it seems like that the metal pieceelectromagnetically couples with the primary-side coil 15, and theprimary-side coil 15 has an actual resistance load, resulting in changeof the primary-side quality factor. Measuring of the quality factorleads to detection of a foreign metal (in an electromagnetically-coupledstate) near the primary-side coil 15.

The power transmitter 10 in the embodiment includes a signal source 11,a capacitor 14, and the primary-side coil 15 (a power transmission coil,an example of a coil). The signal source 11 includes an AC power source12 generating an AC signal (a sine wave) and a resistance element 13.The resistance element 13 indicates an internal resistance (outputimpedance) of the AC power source 12 in illustration. The capacitor 14and the primary-side coil 15 are connected to the signal source 11 toform a serial resonance circuit (an example of a resonance circuit). Acapacitance value (C value) of the capacitor 14 and an inductance value(L value) of the primary-side coil 15 are adjusted in order to resonateat a frequency to be measured. A power transmission section includingthe signal source 11 and the capacitor 14 uses a load modulation systemor the like to transmit power to the outside with no contact through theprimary-side coil 15.

When a voltage between the primary-side coil 15 and the capacitor 14which configure the serial resonance circuit is V1 (an example of avoltage applied to the resonance circuit) and a voltage between bothends of the primary-side coil 15 is V2, the quality factor of the serialresonance circuit is expressed by an expression (5).

$\begin{matrix}\left\lbrack {{Numerical}\mspace{14mu} {Expression}\mspace{14mu} 5} \right\rbrack & \; \\{Q = {\frac{V\; 2}{V\; 1} = \frac{2\pi \; {fL}}{r_{s}}}} & (5)\end{matrix}$

where r_(s) is an effective resistance value at the frequency f.

The voltage V2 is obtained by multiplying the voltage V1 by Q. As themetal piece approaches the primary-side coil 15, the effectiveresistance value r_(s) is increased and the quality factor is decreased.In this way, when the metal piece approaches the primary-side coil 15,the quality factor to be measured (in the electromagnetically-coupledstate) is changed. By detecting the change, the metal piece existingnear the primary-side coil 15 is detectable.

The above-described measurement principle is applied to the powerreceiver (on the secondary side) to allow the power receiver to measurethe quality factor. However, if the power feeding is performed duringthe quality factor measurement, large power is generated in the coil ofthe power receiver due to the magnetic field output from the powertransmission side, and thus the voltage V2 is not normally measured.Accordingly, the quality factor is not obtained precisely, which resultsin less-accurate detection of a foreign metal.

To solve the above-described disadvantage, power feeding needs to besuspended during the measurement. However, if the power feeding isstopped, a large battery operating the circuit for measuring thesecondary-side quality factor is necessary. In addition, when a batteryis mounted on the power receiver as the other measure, a product life isaffected thereby, and detection of a foreign metal is not performed whenthe battery of the mobile device is empty and charging is necessaryimmediately.

Accordingly, the inventors invent an electromagnetic coupling statedetection technology without a battery, in which the quality factormeasurement is performed on the secondary side with use of the powersupplied from the primary side, whereas the secondary side does notperform the quality factor measurement at the time of receiving powerfrom the primary side.

[Configuration of First Embodiment]

(Configuration Example of Power Transmitter)

The configuration example of the power transmitter (on the primary side)according to the first embodiment of the disclosure is described.

FIG. 5 is a block diagram illustrating an internal configuration exampleof the power transmitter according to the first embodiment of thedisclosure. With use of a detection circuit illustrated in the blockdiagram, a conductor such as a metal (a foreign metal) is detected. Thepower transmitter provided with the detection circuit is an example ofan electromagnetic-coupling state detection device.

The detection circuit in the embodiment includes rectification sections21A and 21B, analog/digital converters (hereinafter, referred to as“ADC”) 22A and 22B, and a main control section 23.

The rectification section 21A converts an AC signal (an AC voltage)which is input from between the signal source 11 and the capacitor 14into a DC signal (DC voltage), and then outputs the converted signal.Likewise, the rectification section 21B converts an AC signal (an ACvoltage) which is input from between the primary-side coil 15 and thecapacitor 14 into a DC signal (a DC voltage), and then outputs theconverted signal. Each of the converted DC signals is output to the ADC22A and 22B.

The ADCs 22A and 22B convert an analog DC signal input from therectification sections 21A and 21B into a digital DC signal,respectively, and then output the digital DC signal to the main controlsection 23.

The main control section 23 is an example of a control section, isconfigured by, for example, a Micro-Processing Unit (MPU), and controlsthe entire power transmitter 10. The main control section 23 hasfunctions as an arithmetic processing section 23A and a determinationsection 23B.

The arithmetic processing section 23A is a block performingpredetermined arithmetic processes. In this embodiment, the arithmeticprocessing section 23A calculates a ratio of the voltage V2 to thevoltage V1 from the DC signals input from the ADCs 22A and 22B, that is,calculates a quality factor, and outputs the calculation result to thedetermination section 23B. In addition, the arithmetic processingsection 23A may acquire information (physical amounts such as a voltagevalue) related to detection of a foreign metal from the power receptionside (the secondary side), and then calculate the secondary-side qualityfactor based on the information.

The determination section 23B compares the calculation result input fromthe arithmetic processing section 23A with a threshold stored in anon-volatile memory 24, to determine presence of a foreign metal nearbybased on the comparison result. Moreover, the determination section 23Bmay compare the above-described power-reception side quality factor withthe threshold to determine presence of a foreign metal nearby.

The memory 24 holds a threshold (Ref_Q1) of the primary-side qualityfactor, which is previously measured in a state where nothing is locatedon or near the secondary-side coil. In addition, the memory 24 holds athreshold (Q_Max) of the secondary-side quality factor which is acquiredfrom the power reception side (the secondary side).

A communication control section 25 is an example of a communicationsection on the primary side, and performs communication with acommunication control section of the power receiver which will bedescribed later. The communication control section 25 performstransmission/reception of information related to detection of a foreignmetal, for example, reception of the quality factor and the voltages V1and V2 of the resonance circuit of the power receiver which includes thesecondary-side coil. Moreover, the communication control section 25instructs the signal source 11 to generate or suspend the AC voltage, inresponse to control of the main control section 23. As a communicationstandard in communication with the power receiver, for example, awireless LAN of IEEE 802.11 standard or Bluetooth (registered trademark)may be used. Note that the configuration in which information istransmitted through the primary-side coil 15 and the secondary-side coilof the power receiver may be employed. In addition, the main controlsection 23 may directly instruct the signal source 11 without thecommunication control section 25.

An input section 26 generates an input signal corresponding to useroperation, and outputs the input signal to the main control section 23.

Incidentally, in this embodiment, the description is made on theconfiguration in which the power transmitter 10 includes the detectioncircuit, which enables detection of a foreign metal based on theprimary-side quality factor and detection of a foreign metal based onthe secondary-side quality factor. The configuration is not limitedthereto, and any other configurations are applicable as long as thepower transmitter 10 includes the communication control section 25 andthe main control section 23 which performs at least arithmeticprocessing and determination processing, and has a function to detect aforeign metal based on the quality factor of the power receiver.

(Configuration Example of Power Receiver)

Next, a configuration example of a power receiver (on the secondaryside) according to the first embodiment of the disclosure is described.

FIG. 6 is a block diagram illustrating an internal configuration exampleof the power receiver applied to a mobile phone and the like. Thedetection circuit illustrated in the block diagram detects a foreignmetal. The power receiver provided with the detection circuit is anexample of an electromagnetic-coupling state detection device. Thedetection circuit is an example of a detection section.

A power receiver 30 in the embodiment includes a secondary-side coil 31and a capacitor 32 connected in parallel to the secondary-side coil 31.A first end of each of the coil 31 and the capacitor 32 which areconnected in parallel is connected to a first end of a capacitor 33, anda second end of the capacitor 33 is connected to a first input end of arectification section 34. In addition, a second end of each of thesecondary-side coil 31 and the capacitor 32 which are connected inparallel is connected to a second input end of the rectification section34.

Moreover, a first output end of the rectification section 34 isconnected to an input end of a first regulator 36 through a secondswitch 39. An output end of the first regulator 36 is connected to aload, and a second output end of the rectification section 34 isconnected to a ground terminal. The first output end of therectification section 34 is also connected to a second regulator 37.

Furthermore, a capacitor 35 is connected in series to a first switch 38,one end of the capacitor 35 is connected to the first output end of therectification section 34, and one end of the first switch 38 isconnected to the second output end of the rectification section 34.

The first regulator 36 controls an output voltage and an output currentto be maintained constant, and supplies a voltage of 5 V, for example,to the load. Likewise, the second regulator 37 supplies a voltage of 3V, for example, to respective blocks including the corresponding switch.

The second end of the capacitor 33 is connected to a third switch 40,and is connected to an AC power source 50 (an oscillation circuit)through the third switch 40, a resistance element 52, and an amplifier51. In addition, the second end of the capacitor 33 is connected to aninput end of an amplifier 44A through a third switch 41. On the otherhand, the first end of the capacitor 33 is connected to an input end ofan amplifier 44B through a third switch 42. In addition, the second endof each of the secondary-side coil 31 and the capacitor 32 which areconnected in parallel is connected to a ground terminal through a thirdswitch 43.

As the first switch 38 (an example of a first switch section), thesecond switch 39 (an example of a second switch section), and the thirdswitches 40 to 43 (an example of a third switch section), a switchingelement such as metal-oxide semiconductor field-effect transistor(MOSFET) is applied.

An output end of the amplifier 44A is connected, within a detectioncircuit 45, to an envelope detection section 45A. The envelope detectionsection 45A detects an envelope of the AC signal (corresponding to thevoltage V1) which is input from the second end of the capacitor 33through the third switch 41 and the amplifier 44A, and supplies thedetected signal to an analog/digital converter (ADC) 46A.

On the other hand, an output end of the amplifier 44B is connected,within the detection circuit 45, to an envelope detection section 45B.The envelope detection section 45B detects an envelope of the AC signal(corresponding to the voltage V2) which is input from the first end ofthe capacitor 33 through the third switch 42 and the amplifier 44B, andsupplies the detected signal to an analog/digital converter (ADC) 46B.

The ADCs 46A and 46B convert an analog detected signal input from theenvelope detection sections 45A and 45B into a digital detected signal,respectively, and then output the digital detected signal to a maincontrol section 47.

The main control section 47 is an example of a control section, isconfigured by, for example, a Micro-Processing Unit (MPU), and controlsthe entire power receiver 30. The main control section 47 has functionsas an arithmetic processing section 47A and a determination section 47B.The main control section 47 supplies a drive signal to each switch (agate terminal of an MOSFET) with use of the power supplied from thesecond regulator 37, and performs ON/OFF control (switching function).

The arithmetic processing section 47A is a block performingpredetermined arithmetic processes. The arithmetic processing section47A calculates a ratio of the voltage V2 to the voltage V1 from thedetected signal input from the ADCs 46A and 46B, that is, calculates thequality factor, and outputs the calculation result to the determinationsection 47B. In addition, the arithmetic processing section 47A maytransmit information (a voltage value and the like) of the inputdetected signal to the power transmission side (the primary side),according to setting. Moreover, the arithmetic processing section 47Aperforms frequency sweep processing during detection processing of aforeign metal (sweep processing function).

The determination section 47B compares the quality factor input from thearithmetic processing section 47A with a threshold stored in anon-volatile memory 48, to determine presence of a foreign metal nearbybased on the comparison result. As will be described later, themeasurement information may be transmitted to the power transmitter 10,and the power transmitter 10 may calculate the secondary-side qualityfactor and determine presence of a foreign metal.

The memory 48 holds a threshold to be compared with the quality factor.The threshold is previously measured in a state where nothing is locatedon or near the secondary-side coil 31.

The amplifiers 44A and 44B, the envelope detection sections 45A and 45B,the ADCs 46A and 46B, the main control section 47 (the arithmeticprocessing section 47A and the determination section 47B), and/or thememory 48, which are subsequent to the amplifiers 44A and 44B, areexamples of components configuring the detection circuit 45.

A communication control section 49 is an example of a communicationsection on the secondary side, and performs communication with thecommunication control section 25 of the power transmitter 10. Thecommunication control section 49 performs transmission/reception ofinformation related to detection of a foreign metal, for example,transmission of the quality factor and the voltages V1 and V2 of theresonance circuit of the power receiver 30 which includes thesecondary-side coil 31. The communication standard applied to thecommunication control section 49 is similar to that applied to thecommunication control section 25 of the power transmitter 10. Note thatthe configuration in which the information is transmitted through thesecondary-side coil 31 and the primary-side coil 15 of the powertransmitter 10 may be available.

The AC power source 50 generates an AC voltage (a sine wave) duringquality factor measurement based on the control signal of the maincontrol section 47, and supplies the AC voltage to the second end of thecapacitor 33 through the amplifier 51 and the resistance element 52.

An input section 53 generates an input signal corresponding to useroperation, and outputs the input signal to the main control section 47.

[Operation of Power Receiver]

The detection circuit of the power receiver 30 configured as describedabove is controlled by ON/OFF switching of three switch groups, that is,the first switch 38, the second switch 39, and the third switches 40 to43. Hereinafter, the operation of the power receiver 30 is describedwith paying attention to switching of respective switches.

First, the power received from the power transmitter 10 through thesecondary-side coil 31 is charged in the capacitor 35 (an example of apower storage section) provided subsequently to the rectificationsection 34. A current value and a time operable by the power charged inthe capacitor are determined by an expression (6).

[Numerical Expression 6]

CV=it  (6)

In the expression (6), C is a capacitance value of the capacitor, V is avoltage value of the capacitor, i is a current value of the capacitor,and t is a time. Specifically, when the voltage value charged in thecapacitor of 10 μF is changed from 9 V to 4 V, for example, the currentof 50 mA is allowed to flow for 1 msec. If the capacitance value of thecapacitor is large, it is possible to flow a large current or to extenda time of current flow.

Incidentally, if the capacitor 35 with a high capacitance value isprovided subsequently to the rectification section 34, defect may occurduring communication between the power receiver 30 and external devices.Therefore, control by the switch 38 is desirable. In other words,conduction between the drain and the source of the first switch 38 ismade and the capacitor 35 is connected only during the quality factormeasurement so that the adverse affect is eliminated.

FIG. 7 illustrates a diagram of a waveform of a state in which thevoltage (the voltage at the input end of the first regulator 36)actually charged in the capacitor 35 drops.

Originally, the voltage at the input end of the first regulator 36 dropsto 0 V when a carrier signal of the power transmitter 10 is stopped. Inthe figure, however, it is confirmed that voltage drop is moderate dueto an electric charge accumulated in the capacitor 35. In example ofFIG. 7, the voltage at the input end of the first regulator 36 graduallydrops from 9.5 V to 8.5 V during carrier suspension period of about 1.8ms.

Accordingly, if the detection section consumes small current to someextent and a time of quality factor measurement is short, the qualityfactor is allowed to be measured while the carrier signal output fromthe power transmitter 10 is suspended. Note that when the carrier signaloutput from the power transmitter 10 is suspended (during the qualityfactor measurement), the load needs to be surely electrically separatedfrom the detection section. For example, such electrical separation iscontrolled by using a P-channel MOSFET as the second switch 39, andusing control in which the power receiver 30 is turned off in responseto the input of the carrier signal or using an enable function of thefirst regulator 36. Disconnection of the load from the detection circuitis not necessary during the charge of the capacitor 35 or communicationthrough the communication control section 49.

At the time of the quality factor measurement, the voltage value betweenboth ends of the capacitor 33 is measured by using a similar method tothe above-described measuring instruments (LCR meter). Specifically, thethird switches 40 to 43 are turned on at the timing of suspension of thecarrier signal, and the quality factor is calculated from two voltagewaveforms which are obtained by rectifying the sine wave output from theAC power source 50 and are detected on the first and second ends of thecapacitor 33. Detection of a foreign metal is performed by comparing thecalculated quality factor with the predetermined threshold.

[Overall Control of Non-Contact Power Transmission System]

Next, overall control of a non-contact power transmission systemaccording to the first embodiment of the disclosure will be described.

FIG. 8 is a flowchart illustrating processing during power feeding ofthe non-contact power transmission system which is configured to includethe power transmitter 10 (see FIG. 5) and the power receiver 30 (seeFIG. 6).

When the power transmitter 10 (on the primary side) is activated and thepower receiver 30 (on the secondary side) is disposed near the powertransmitter 10, negotiation is performed between the power transmitter10 and the power receiver 30. Power feeding is started after the powertransmitter 10 and the power receiver 30 recognizes the other side witheach other. The power transmitter 10 or the power receiver 30 performsthe quality factor measurement at the time of starting power feeding,and determines whether the current quality factor measurement is a firsttime measurement (step S1).

For example, if the measurement is performed immediately after the powertransmitter 10 or the power receiver 30 is turned on, the respectivedevices determine that the current quality factor measurement is thefirst time measurement. Alternatively, as a result of the negotiation,when the power receiver 30 is identified as a first communicationpartner from ID information (identification information) of the powerreceiver 30, the power transmitter 10 determines that the currentquality factor measurement is a first time measurement. Stillalternatively, at the time of the negotiation, the power transmitter 10may receive, from the power receiver 30, the result of the number oftimes of the quality factor measurement which is calculated by the powerreceiver 30, and perceives the number of times of the quality factormeasurement.

As still another example, the determination may be made by using a timeelapsed from the previous quality factor measurement. The powertransmitter 10 (and the power receiver 30) has a clock section (notillustrated), and when performing the quality factor measurement, thepower transmitter 10 (and the power receiver 30) stores, in the memory24 (and the memory 48), the measured quality factor which iscorresponded to the measurement time. Then, the power transmitter 10(and the power receiver 30) compares the time of the previous qualityfactor measurement with the time of the current quality factormeasurement, and when the time difference exceeding a predeterminedvalue is detected, the current quality factor measurement is determinedas the first time measurement. For example, quality factor measurementwith frequency sweep is defined as the first time measurement, and thenumber of times of the quality factor measurement is determined withreference to the defined first measurement. Note that a timer functionof the clock section may be activated at the time of the previousquality factor measurement, and the number of times of the qualityfactor measurement may be determined based on the elapsed time of thetimer.

When the quality factor measurement is determined as the firstmeasurement, the power receiver 30 uses the plurality of frequencies forthe measurement test signals (sine wave) output from the AC power source50 (sweep measurement), and acquires the largest quality factor from theplurality of obtained secondary-side quality factors (step S2). Thefrequency of the test signal at the largest quality factor is stored inthe memory. The detail of the process in the step S2 will be describedlater.

To measure the quality factor, a sine wave of the resonance frequencyneeds to be input to the power receiver 30. However, the resonancefrequency is changed due to variation of quality of components in thepower receiver 30, variation of a positional relationship between themounted coil and a metal inside of the device (for example, a housing),environment around the secondary-side coil 31, the contained foreignmetal, and the like. Therefore, in consideration of the shift of theresonance frequency, the resonance frequency needs to be found byperforming measurement (frequency sweep) with use of a plurality ofdifferent frequencies within an appropriate range (measurement range).Although the frequency sweep is necessary for the first quality factormeasurement, may be omitted for second and subsequent quality factormeasurement, in consideration of the entire non-contact powertransmission system. As an example where the frequency sweep is omittedin the second and subsequent quality factor measurement, the case wherethe positional relationship between the power transmitter 10 and thepower receiver 30 is not largely changed from that of the first qualityfactor measurement is exemplified.

On the other hand, in the case where the current quality factormeasurement is not determined as the first measurement in thedetermination process at the step S1, the power receiver 30 acquires thequality factor with use of a test signal of a frequency determined inthe first quality factor measurement (step S3). The detail of theprocess in the step S3 will be described later.

The power transmitter 10 or the power receiver 30 determines whetherthere is a possibility that a foreign metal is present, based on thesecondary-side quality factor (step S4). When there is no possibilitythat a foreign metal is present, the process proceeds to a step S6.

On the other hand, when there is a possibility that a foreign metal ispresent in the determination process in the step S4, the processproceeds to the step S2, and the power receiver 30 performs frequencysweep of the test signal to acquire the largest quality factor from theplurality of secondary-side quality factors.

After the process in the step S2 is finished, the power transmitter 10or the power receiver 30 determine the presence of a foreign metal basedon the secondary-side quality factor obtained by calculation (step S5).When a foreign metal is present, the power feeding is forciblyterminated or an alert is given to a user, as a finishing process. Thepower feeding is forcibly terminated by stopping power transmission ofthe power transmitter 10, or stopping power reception of the powerreceiver 30 even if the power transmitter continues the powertransmission.

The quality factor measurement in the above-described steps S2 to S5 isperformed with use of the power charged in the power storage section(the capacitor 35). For example, in the case of frequency sweep, afterthe electric charges are charged in the capacitor 35 by an amount ofenabling quality factor (namely, voltages V1 and V2) measurement for atest signal of one frequency, the quality factor measurement, charging,and the quality factor measurement for the test signal of the subsequentfrequency are repeated.

Then, when a foreign metal is not detected in the step S5, power feedingfrom the power transmitter 10 to the power receiver 30 is performed fora predetermined time (step S6).

Finally, the power receiver 30 determines whether the battery or thelike (load, not illustrated) has been fully charged, and transmits thedetermination result to the power transmitter 10 (step S7). When thebattery has been fully charged, the charging process is terminated, andwhen the battery has not been fully charged, the process returns to thestep S1 and repeats the above-described processes. Note that thedetermination and the communication about the full charge may beperformed during power feeding.

As described above, the frequency sweep is performed only in the firstquality factor measurement, and the quality factor in the second andsubsequent measurement is measured only for a test signal of a frequencywhich is determined as optimum in the first quality factor measurement.However, in the case where it is determined in the second and subsequentquality factor measurement that there is a possibility that a foreignmetal is present, the frequency is swept again and determination isperformed because there is a possibility of frequency shift due to thechange of the positional relationship between the primary-side coil andthe secondary-side coil. When the presence of a foreign metal isdetermined even if the frequency is swept, the power feeding is forciblyterminated or an alert is given to a user. This method significantlydecreases the time of the quality factor measurement.

[Example of Performing Quality Factor Measurement with Frequency Sweepon Primary Side]

Next, processing in a case where the quality factor measurement with afrequency sweep in the step S2 is performed on the primary side isdescribed. Since the frequency sweep is performed, it is assumed thatthe quality factor measurement is determined as the first timemeasurement. The processing is considered to be performed in the casewhere the power transmitter 10 determines that the current qualityfactor measurement is the first time measurement or in the case wherethe power receiver 30 determines the current quality factor measurementis the first time measurement and transmits the result to the powertransmitter 10.

FIG. 9 is a flowchart illustrating processing in the case where qualityfactor measurement reflecting a frequency sweep is performed on theprimary side (the power transmitter 10).

First, after completing the negotiation with the main control section 47of the power receiver 30, the main control section 23 of the powertransmitter 10 outputs electromagnetic waves from the primary-side coil15 to start power transmission (transmission of a carrier signal) to thepower receiver 30 (step S11). The main control section 47 of the powerreceiver 30 receives the electromagnetic waves output from the powertransmitter 10 through the secondary-side coil 31 to start powerreception (step S12).

Upon starting the power transmission, the main control section 23 of thepower transmitter 10 transmits a command of first quality factormeasurement to the power receiver 30 through the communication controlsection 25 (step S13). The main control section 47 of the power receiver30 receives the command of first quality factor measurement from thepower transmitter 10 through the communication control section 49 (stepS14).

FIG. 10 is an operation timing chart in the non-contact powertransmission system according to the first embodiment of the disclosure.

In the embodiment, a “quality-factor measurement period (61-1, 61-2, and61-3)” for performing quality factor measurement and a “power supplyperiod (62)” for performing processing such as power supply (other thanquality factor measurement) are alternately set. When the communicationbetween the power transmitter 10 and the power receiver 30 isestablished, the main control section 23 of the power transmitter 10issues the command of first quality factor measurement in the step S13.The command of first quality factor measurement is transmitted at thehead of the first quality-factor measurement period 61-1, for example.The first quality-factor measurement period is divided into a pluralityof periods including “charging”, “quality factor measurement atfrequency f₁”, “charging”, “quality factor measurement at frequency f₂”,. . . , “quality factor measurement at frequency f_(n-1)”, “charging”,“quality factor measurement at frequency f_(n)”, “charging”, and“transmission to primary side”.

The main control section 47 of the power receiver 30 switches the firstswitch 38, the second switch 39, and the third switches 40 to 43 betweenON and OFF, so as to correspond to the plurality of periods. The mainswitching timings of the first switch 38, the second switch 39, and thethird switches 40 to 43 are described below.

1. The first switch 38 is turned on during a quality-factor measurementperiod (charge the capacitor 35), and is turned off during the otherperiods (power supply period).2. The second switch 39 is turned off during a quality-factormeasurement period, and is turned on during the other periods (powersupply period).3. The third switches 40 to 43 are turned on during a quality-factormeasurement period (specifically, at the time of detecting the voltagesV1 and V2), and are turned off during the other periods.

When receiving the command of first quality factor measurement, the maincontrol section 47 of the power receiver 30 turns the first switch 38on, electrically connects the rectification section 34 to the capacitor35, and charges the power received from the primary side. At this time,the main control section 47 of the power receiver 30 turns the secondswitch 39 off, and disconnects the first regulator 36, that is, the loadfrom the capacitor 35 (step S15).

Subsequently, the AC power source 50 of the power receiver 30 outputs atest signal (a sine wave) for measurement in response to control of themain control section 47. The frequency Freq of the test signal at thistime is set to an initial value f₁ (step S16).

The main control section 23 of the power transmitter 10 suspends powertransmission (transmission of the carrier signal) to the power receiver30 (step S17). The latency time after the power transmission start inthe step S13 until the power transmission suspension in the step S17 isequal to or longer than at least a time necessary for charging thecapacitor 35 with desired power (the power necessary for quality factormeasurement at one frequency).

The main control section 47 of the power receiver 30 suspends the powerreception in response to the suspension of the power transmission fromthe power transmitter 10 (step S18).

At this time, the main control section 47 turns the third switches 40 to43 on (step S19). Upon turning the third switch 40 on, the test signalof the frequency f₁ generated in the AC power source 50 is supplied tothe second end of the capacitor 33 through the third switch 40. Inaddition, upon turning the third switch 41 on, the second end of thecapacitor 33 is conducted with the input end of the amplifier 44A, andupon turning the third switch 42 on, the first end of the capacitor 33is conducted with the input end of the amplifier 44B.

Then, the main control section 47 detects the voltage V1 at the secondend of the capacitor 33 through the amplifier 44A, the envelopedetection section 45A, and the ADC 46A, and records the voltage V1 inthe memory 48. Likewise, the main control section 47 detects the voltageV2 at the first end of the capacitor 33 through the amplifier 44B, theenvelope detection section 45B, and the ADC 46B, and records the voltageV2 in the memory 48 (step S20).

After acquiring the voltages V1 and V2 for the test signal of thefrequency f₁, the main control section 47 turns the third switches 40 to43 off (step S21).

At this time, the main control section 23 of the power transmitter 10restarts the power transmission to the power receiver 30 (step S22). Thelatency time after the power transmission suspension in the step S17until the power transmission start in the step S22 is equal to or longerthan at least a time necessary for detecting and recording the voltagesV1 and V2. Then, after the power transmission to the power receiver 30is restarted in the step S22, the process returns to the step S17 afterthe lapse of the latency time of charging the capacitor 35, and the maincontrol section 23 of the power transmitter 10 suspends the powertransmission again. The latency time after the power transmission startin the step S22 until the power transmission suspension in the step S17is equal to or longer than at least a time necessary for charging thecapacitor 35 with desired power.

The main control section 47 of the power receiver 30 starts the powerreception from the power transmitter 10 in response to restart of thepower transmission of the power transmitter 10, and charges thecapacitor 35 (step S23). During the latency time for charging thecapacitor 35, the AC power source 50 of the power receiver 30 outputs atest signal of a subsequent frequency Freq in response to the control ofthe main control section 47 (step S24). The frequency Freq of the testsignal at this time is f₂.

After the process in the step S24 is completed, the process returns tothe step S18 after the lapse of the latency time for charging thecapacitor 35, and the main control section 47 of the power receiver 30suspends the power reception in response to suspension of the powertransmission from the power transmitter 10. Then, the main controlsection 47 of the power receiver 30 continues the processes subsequentto the step S19, performs the quality factor measurement with use of thetest signal of the frequency f₂, and acquires the voltages V1 and V2.

During the period after the power reception suspension in the step S18until the power reception start in the step S23 (steps S19 to S21), eachblock in the detection circuit is operated only by the power charged inthe capacitor 35.

After the process (frequency sweep) of acquiring the voltages V1 and V2for each test signal of the respective frequencies is completed, themain control section 47 of the power receiver 30 turns the first switch38 off, and disconnects the capacitor 35 from the detection circuit(step S25). Subsequently, the main control section 47 of the powerreceiver 30 controls the AC power source 50 to stop the output of thetest signal (step S26).

Then, the main control section 47 of the power receiver 30 responds tothe command of first quality factor measurement from the powertransmitter 10. As a response, the main control section 47 of the powerreceiver 30 sends back the threshold used for determination of a foreignmetal and the measurement data group (Freq, V1, and V2) obtained withuse of the test signals of the respective frequencies, which are storedin the memory 48, to the power transmitter 10 through the communicationcontrol section 49 (step S27).

Incidentally, in the flowchart illustrated in FIG. 9, the second switch39 is turned off and the first regulator 36 (load) is disconnected fromthe capacitor 35 (see step S15) while the capacitor 35 is charged.However, the load may be fed with the power while the capacitor 35 ischarged. The power feeding (charge to the capacitor 35) needs to besuspended at least during the quality factor measurement (specifically,at the time of detecting the voltages V1 and V2), and the power feedingmay be continued or suspended during communication or while thecapacitor 35 is charged. The same applies to the other flowchart whichwill be described below (FIG. 12, FIG. 13, and FIG. 14).

After process in the step S27, the power transmitter 10 receives thethreshold and the measurement data group (Freq, V1, and V2) from thepower receiver 30, and stores the threshold and the measurement datagroup in the memory 24 (step S28).

Then, the arithmetic processing section 23A of the power transmitter 10calculates the secondary-side quality factor from the voltages V1 and V2for each frequency Freq of the test signals received from the powerreceiver 30, based on the expression (5), creates a table of thefrequencies and the quality factors, and stores the table in the memory24. FIG. 11 graphically illustrates the relationship between thefrequencies of the test signals and the quality factors. The largestsecondary-side quality factor (Q_Max) is determined (step S29). In theexample of FIG. 11, Q_Max is a quality factor at the frequency f₀ nearthe maximum value in the frequency characteristic curve of the qualityfactor.

Next, the determination section 23B of the power transmitter 10 comparesQ_Max with the threshold stored in the memory 24 to determine whetherQ_Max is lower than the threshold (step S30).

When Q_Max is lower than the threshold in the determination process inthe step S30, the determination section 23B determines that a foreignmetal is present (the step S5 in FIG. 8), and performs completionprocessing. On the other hand, when Q_Max is not lower than thethreshold, the determination section 23B determines that a foreign metalis absent (the step S5 in FIG. 8), and the process proceeds to the stepS6.

In the measurement results illustrated in Table 2, the quality factorhas a difference by at least 25% between with a foreign metal andwithout a foreign metal. Therefore, the value obtained by subtracting25% from the quality factor with a foreign metal may be used as thethreshold, for example. The value is merely an example, and the value isdesirably set appropriately according to the measurement target becausethe change amount of the quality factor is different depending on thestructure of the power receiver, environment, the size and kind of aforeign metal to be detected.

[Example of Calculating Quality Factor Reflecting Frequency Sweep onSecondary Side]

Next, processing in the case where the quality factor reflecting afrequency sweep in the step S2 is calculated on the secondary side isdescribed. Since the frequency sweep is performed, it is assumed thatthe quality factor measurement is determined as the first timemeasurement, similarly to the flowchart in FIG. 9.

FIG. 12 is a flowchart illustrating processing in the case where qualityfactor measurement reflecting a frequency sweep is performed on thesecondary side (the power receiver 30).

The processes in steps S41 to 56 in FIG. 12 are the same as those in thesteps S11 to S26 in FIG. 9, and thus the description thereof is omitted.

After output of the test signal is stopped in the step S56, thearithmetic processing section 47A of the power receiver 30 calculatesthe secondary-side quality factor from the voltages V1 and V2 for eachfrequency Freq of the test signals, based on the expression (5), createsa table of the frequencies and the quality factors, and stores the tablein the memory 48. Then, the arithmetic processing section 47A of thepower receiver 30 determines the largest secondary-side quality factor(Q_Max) (step S57).

Next, the determination section 47B of the power receiver 30 comparesQ_Max with the threshold stored in the memory 48 to determine whetherQ_Max is lower than the threshold (step S58).

In the determination process in the step S58, when Q_Max is lower thanthe threshold, the determination section 47B determines a foreign metalis present. On the other hand, when Q_Max is not lower than thethreshold, the determination section 47B determines a foreign metal isabsent.

Then, the main control section 47 of the power receiver 30 responds tothe command of first quality factor measurement from the power receiver10. As a response, the main control section 47 of the power receiver 30sends back the determination result of a foreign metal to the powertransmitter 10 through the communication control section 49 (step S59).

The power transmitter 10 receives the determination result of a foreignmetal from the power receiver 30 (step S60).

Then, the determination section 23B of the power transmitter 10 uses thedetermination result of a foreign metal received from the power receiver30 to determine the presence of a foreign metal (step S61).

In the determination process in the step S61, the determination section23B performs a completion process when the received determination resultindicates the presence of a foreign metal (step S5 in FIG. 8). On theother hand, when the determination result indicates the absence of aforeign metal (step S5 in FIG. 8), the process proceeds to the step S6.

As described above, both in the case where the quality factor iscalculated in the power transmitter 10 (on the primary side) and in thecase where the quality factor is calculated in the power receiver 30 (onthe secondary side), the threshold to be compared with the calculatedquality factor is held by the power receiver 30. When the calculation isperformed in the power transmitter 10, the threshold is transmittedtogether with the voltage value because various devices are used as thepower receiver 30 and the threshold is expected to be varied dependingon the device.

As illustrated in FIG. 9, when the power transmitter 10 (on the primaryside) performs calculation of the quality factor and determination of aforeign metal, it is advantageous that the power receiver 30 (on thesecondary side) needs not have hardware for an arithmetic processingsection and a determination section. For example, a mobile device usedas the power receiver 30 is expected to be reduced in size, weight, andcost.

On the other hand, as illustrated in FIG. 12, when the power receiver 30(on the secondary side) performs calculation of the quality factor anddetermination of a foreign metal, the power receiver 30 (on thesecondary side) needs to have hardware for an arithmetic processingsection and a determination section. Incidentally, only information ofthe determination result indicating the presence or absence of a foreignmetal is transmitted to the power transmitter 10 (on the primary side).Accordingly, the information amount is small and thus communication timeis expected to be reduced.

[Example of Performing Second and Subsequent Quality Factor Measurementon Primary Side]

Next, processing in the case where second and subsequent quality factormeasurement is performed on the primary side is described. In thisexample, although the case where second quality factor measurement aftera frequency sweep is performed is described, the same applies to a thirdand subsequent quality factor measurement.

FIG. 13 is a flowchart illustrating processing in the case where qualityfactor measurement is preformed on the primary side (the powertransmitter).

Processes in steps S71 to S85 in FIG. 13 correspond to processes in thesteps S11 to S26 (without step S24) in FIG. 9, and thus different pointsbetween FIG. 9 and FIG. 13 will be described mainly.

When the power transmission is started in the steps S71 and S72, themain control section 23 of the power transmitter 10 transmits a commandof second quality factor measurement to the power receiver 30 throughthe communication control section 25 (step S73). The main controlsection 47 of the power receiver 30 receives the command of secondquality factor measurement from the power transmitter 10 through thecommunication control section 49 (step S74).

The command of second quality factor measurement is transmitted at thehead of a second quality-factor measurement period 61-2 (see FIG. 10),for example. The second quality-factor measurement period 61-2 isdivided into four periods including “charging”, “quality factormeasurement at frequency f₀”, “charging”, and “transmission to primaryside”. The main control section 47 of the power receiver 30 switches thefirst switch 38, the second switch 39, and the third switches 40 to 43between ON and OFF, so as to correspond to the four periods.

When receiving the command of second quality factor measurement, themain control section 47 of the power receiver 30 turns the first switch38 on, and connects the capacitor 35 to the detection circuit forcharging. At this time, the main control section 47 of the powerreceiver 30 turns the second switch 39 off, and disconnects the firstregulator 36, that is, the load from the capacitor 35 (step S75).

Subsequently, the AC power source 50 of the power receiver 30 outputs atest signal (a sine wave) for measurement in response to control of themain control section 47. The frequency Freq of the test signal at thistime is set to the frequency f₀ (≈a resonance frequency) at which thelargest quality factor (Q_Max) is obtained in the previous frequencysweep processing (step S76).

The main control section 23 of the power transmitter 10 suspends powertransmission (transmission of the carrier signal) to the power receiver30 (step S77). The latency time after the power transmission start inthe step S73 until the power transmission suspension in the step S77 isequal to or longer than at least a time necessary for charging thecapacitor 35 with desired power (the power necessary for quality factormeasurement at one frequency).

The main control section 47 of the power receiver 30 suspends the powerreception in response to the suspension of the power transmission fromthe power transmitter 10 (step S78).

At this time, the main control section 47 turns the third switches 40 to43 on (step S79). Then, the main control section 47 detects the voltageV1 at the second end of the capacitor 33, and stores the voltage V1 inthe memory 48. At the same time, the main control section 47 detects thevoltage V2 at the first end of the capacitor 33, and stores the voltageV2 in the memory 48 (step S80). After acquiring the voltages V1 and V2for the test signal of the frequency f₀, the main control section 47turns the third switches 40 to 43 off (step S81).

At this time, the main control section 23 of the power transmitter 10restarts the power transmission to the power receiver 30 (step S82). Thelatency time after the power transmission suspension in the step S77until the power transmission start in the step S82 is equal to or longerthan at least a time necessary for detecting and recording the voltagesV1 and V2. In FIG. 9, after the power transmission to the power receiver30 is restarted, the power transmission is suspended again after thelapse of the latency time of charging the capacitor 35. In this example,however, the power transmission is not suspended again because onlyacquisition of the measurement data for the test signal of the frequencyf₀ is necessary.

The main control section 47 of the power receiver 30 starts the powerreception from the power transmitter 10 in response to restart of thepower transmission of the power transmitter 10, and charges thecapacitor 35 (step S83).

In FIG. 9, although a test signal of the subsequent frequency Freq (f₂)is output during the latency time for charging the capacitor 35 (seestep S24), it is not performed in this example.

After the process of acquiring the voltages V1 and V2 for the testsignal of the frequency f₀ is completed, the main control section 47 ofthe power receiver 30 turns the first switch 38 off, and disconnects thecapacitor 35 from the detection circuit (step S84). Subsequently, themain control section 47 of the power receiver 30 controls the AC powersource 50 to stop the output of the test signal (step S85).

Then, the main control section 47 of the power receiver 30 responds tothe command of second quality factor measurement from the powertransmitter 10. As a response, the main control section 47 of the powerreceiver 30 sends back the threshold used for determination of a foreignmetal and the measurement data group (f₀, V1, and V2) for the testsignal of the frequency f₀, which are stored in the memory 48, to thepower transmitter 10 through the communication control section 49 (stepS86).

The power transmitter 10 receives the threshold and the measurement datagroup (f₀, V1, and V2) from the power receiver 30, and stores thethreshold and the measurement data group in the memory 24 (step S87).

Then, the arithmetic processing section 23A of the power transmitter 10calculates the secondary-side quality factor from the voltages V1 and V2for the test signal of the frequency f₀ received from the power receiver30, based on the expression (5) (step S88).

Subsequently, the determination section 23B of the power transmitter 10compares the calculated secondary-side quality factor with Q_Max at thefrequency sweep stored in the memory 24 to determine whether the qualityfactor is within a predetermined range of Q_Max. As a specific example,the determination section 23B of the power transmitter 10 determineswhether the quality factor is lower than Q_Max by X % (step S89). Inother words, Q_Max at the previous frequency sweep is used as areference quality factor for detecting a foreign metal.

In the determination process in the step S89, when the quality factor islower than Q_Max by X % or more, the determination section 23Bdetermines that there is a possibility that a foreign metal is present(step S4 in FIG. 8), and the process proceeds to the step S2. On theother hand, when the quality factor is not lower than Q_Max by X %, thedetermination section 23B determines that a foreign metal is absent(step S4 in FIG. 8), and the process proceeds to the step S6.

In the above-described determination process, when the quality factor islower than Q_Max by X % or more, it is determined that there is apossibility that a foreign metal is present. This is because, asdescribed above, there is a possibility of frequency shift due to thechange of a positional relationship between the primary-side coil andthe secondary-side coil. In other words, the frequency in the secondquality factor measurement may be shifted from the resonance frequencyf₀ determined in the first quality factor measurement (frequency sweep).Therefore, there is a possibility that the quality factor (Q_Max) at theresonance frequency f₀ obtained in the first quality factor measurement(frequency sweep) is largely different from the quality factor obtainedin the second quality factor measurement with use of the resonancefrequency f₀. Accordingly, when the quality factor obtained in thesecond quality factor measurement is lower than Q_Max by X % or more, itis determined that there is a possibility of a foreign metal, andprocess proceeds to the step S2 to perform frequency sweep processingagain for secure determination of a foreign metal.

[Example of Performing Second and Subsequent Quality Factor Calculationon Secondary Side]

Next, processing in the case where second and subsequent quality factormeasurement is performed on the secondary side is described. In thisexample, the case where second quality factor measurement after afrequency sweep is described.

FIG. 14 is a flowchart illustrating processing in the case where qualityfactor calculation is performed on the secondary side (the powerreceiver).

Processes in steps S91 to 5105 in FIG. 14 are the same as those in thesteps S71 to S85 in FIG. 13, and thus the description thereof will beomitted.

After the output of the test signal is stopped in the step S105, thearithmetic processing section 47A of the power receiver 30 calculatesthe secondary-side quality factor from the voltages V1 and V2 for thetest signal of the frequency f₀, based on the expression (5) (stepS106).

Next, the determination section 47B of the power receiver 30 comparesthe calculated secondary-side quality factor with Q_Max (referencequality factor) at the previous frequency sweep stored in the memory 48to determine whether the quality factor is lower than Q_Max by X % (stepS107).

In the determination process in the step S107, when the quality factoris lower than Q_Max by X % or more, the determination section 47Bdetermines that there is a possibility that a foreign metal is present.On the other hand, when the quality factor is not lower than Q_Max by X%, the determination section 47B determines that a foreign metal isabsent.

Then, the main control section 47 of the power receiver 30 responds tothe command of second quality factor measurement from the powertransmitter 10. As a response, the main control section 47 of the powerreceiver 30 sends back the determination result of a foreign metal tothe power transmitter 10 through the communication control section 49(step S108).

The power transmitter 10 receives the determination result of a foreignmetal from the power receiver 30 (step S109).

Then, the determination section 23B of the power transmitter 10 uses thedetermination result of a foreign metal received from the power receiver30 to determine the presence of a foreign metal (step S110).

In the determination process in the step S110, when the receiveddetermination result indicates that there is a possibility that aforeign metal is presence (step S4 in FIG. 8), the process of thedetermination section 23B returns to the step S2. On the other hand,when the received determination result indicates that a foreign metal isabsent (step S4 in FIG. 8), the process of the determination section 23Bproceeds to the step S6.

As illustrated in FIG. 13 and FIG. 14, the second and subsequent qualityfactor measurement is preformed with use of the frequency f₀ and thequality factor determined in the first quality factor measurement(determination process of a foreign metal) so that a time of qualityfactor measurement for detecting a foreign metal with respect to thetime of power feeding is allowed to be reduced (see FIG. 10).

In the above-described first embodiment, the influence of a metalhousing on a secondary-side (mobile phone and the like) is eliminated byusing the secondary-side quality factor for detection of a foreignsubstance. Accordingly, compared with detection of a foreign substanceby typical DC-DC efficiency, detection accuracy of a foreign metal isallowed to be improved.

In addition, power is charged in the capacitor and the detection circuitis driven by the power whenever the quality factor is measured so thatthe quality factor is allowed to be measured without using asecondary-side battery when the power feeding from the primary side tothe secondary side is not performed. Therefore, a large battery fordetecting a foreign metal or a complicated circuit for controlling itspower is not necessary on the secondary side, and thus a mobile deviceand the like is expected to be reduced in size, weight, and cost.

Moreover, by appropriately switching the third switches 40 to 43 in thepower feeding and the quality factor measurement, interference between ameasurement signal (a sine wave signal) used in the quality factormeasurement, which is output from the AC power source on the secondaryside, and a power feeding signal fed from the primary side is prevented,and thus quality factor is calculated with high accuracy.

In the embodiment, although a capacitor is used as a power storagesection for storing electric charges to be consumed in the qualityfactor measurement, a power storage means other than a capacitor, forexample, a small secondary battery may be used.

[Examples of Other Resonance Circuit]

Incidentally, in the embodiment, an example in which the powertransmitter 10 includes a serial resonance circuit is described.However, any other resonance circuits may be used as a resonancecircuit. Examples thereof are illustrated in FIGS. 15A and 15B. In theexample of FIG. 15A, a capacitor 14A is connected in series with aparallel resonance circuit of a capacitor 14B and the primary-side coil15 to configure a resonance circuit. Moreover, in the example of FIG.15B, the capacitor 14B is connected in parallel with a serial resonancecircuit of the capacitor 14A and the primary-side coil 15 to configure aresonance circuit. A detection section calculates a primary-side qualityfactor with use of a voltage V1 between the primary-side coil 15 and thecapacitor 14A and a voltage V2 between both ends of the primary-sidecoil 15. Both the voltages V1 and V2 are obtained in the resonancecircuit illustrated in FIGS. 15A and 15B. The serial resonance circuitand the other resonance circuits described above are merely examples,and the configuration of the resonance circuit is not limited to theexamples. Similarly to the power transmitter 10, various resonancecircuits may apply to the power receiver 30. In FIG. 6, the resonancecircuit illustrated in FIG. 15A is applied.

2. Second Embodiment

In the first embodiment, the arithmetic processing sections 23A and 47Adetermine the quality factor from the voltage V1 between theprimary-side coil and the capacitor in the serial resonance circuit andthe voltage V2 between both ends of the power transmission coil. In thesecond embodiment, the quality factor is determined by a half bandwidthmethod.

In the half bandwidth method, in the case where a serial resonancecircuit is configured, a quality factor is determined by an expression(7) from a band (between frequencies f1 and f2) in which the impedanceis 12 times an absolute value of an impedance (Zpeak) at a resonancefrequency f₀ as illustrated in a graph of FIG. 16.

$\begin{matrix}\left\lbrack {{Numerical}\mspace{14mu} {Expression}\mspace{14mu} 7} \right\rbrack & \; \\{Q = \frac{f_{0}}{f_{2} - f_{1}}} & (7)\end{matrix}$

In addition, in the case where a parallel resonance circuit isconfigured, a quality factor is determined by the expression (7) from aband (between frequencies f1 and f2) in which the impedance is 1/√2times an absolute value of an impedance (Zpeak) at a resonance frequencyf₀ as illustrated in a graph of FIG. 17.

3. Third Embodiment

Unlike the first and second embodiments, a third embodiment is anexample where the arithmetic processing section 23A or 47A calculates aquality factor from a ratio of an imaginary component to a realcomponent of impedance of a resonance circuit. In the third embodiment,the real component and the imaginary component of the impedance aredetermined with use of a self-balancing bridge circuit and a vectorratio detector.

FIG. 18 is a circuit diagram of a self-balancing bridge for calculatinga quality factor from the ratio of the imaginary component to the realcomponent of the impedance, according to the third embodiment.

A self-balancing bridge circuit 70 illustrated in FIG. 18 has aconfiguration similar to a well-known inverting amplifier circuit. Aninverting input terminal (−) of an inverting amplifier 73 is connectedto a coil 72, and a non-inverting input terminal (+) is grounded. Then,a feedback resistance element 74 gives a negative feedback to theinverting input terminal (−) through an output terminal of the invertingamplifier 73. In addition, an output (a voltage V1) of an AC powersource 71 which inputs an AC signal to the coil 72, and an output (avoltage V2) of the inverting amplifier 73 are input to a vector ratiodetector 75. The coil 72 corresponds to the primary-side coil 15 in FIG.5 or the secondary-side coil 31 in FIG. 6.

The self-balancing bridge circuit 70 operates so that the voltage at theinverting input terminal (−) is constantly zero by a function of thenegative feedback. Moreover, a current flowing from the AC power source71 to the coil 72 has large input impedance of the inverting amplifier73 so that almost all current flow in the feedback resistance element74. As a result, the voltage applied to the coil 72 is equal to thevoltage V1 of the AC power source 71, and the output voltage of theinverting amplifier 73 is a product of a feedback resistance value Rsand a current I flowing through the coil 72. The feedback resistancevalue Rs is a known reference resistance value. Therefore, the impedanceis determined by detecting the voltages V1 and V2 and calculating aratio therebetween. The vector ratio detector 75 uses phase informationof the AC power source 71 (illustrated by an alternate long and shortdash line) in order to determine the voltages V1 and V2 as complexnumbers.

In the embodiment, a real component R_(L) and an imaginary componentX_(L) of impedance Z_(L) of the resonance circuit are determined withuse of the self-balancing bridge circuit 70, the vector ratio detector75, and the like, and a quality factor is determined from the ratio. Thefollowing expressions (8) and (9) illustrate processes for determining aquality factor.

$\begin{matrix}\left\lbrack {{Numerical}\mspace{14mu} {Expression}\mspace{14mu} 8} \right\rbrack & \; \\{Z_{L} = {{R_{L} + {jX}_{L}} = {\frac{V\; 1}{I} = {\frac{V\; 1}{V\; 2}{Rs}}}}} & (8) \\\left\lbrack {{Numerical}\mspace{14mu} {Expression}\mspace{14mu} 9} \right\rbrack & \; \\{Q = \frac{X_{L}}{R_{L}}} & (9)\end{matrix}$

4. Others

Incidentally, in the above-described first to third embodiments,description is made on an assumption of a non-contact power transmissionsystem of a magnetic field resonance type. However, the disclosure isintended to perform detection of a foreign metal existing between apower transmission side and a power reception side, and improvedetection accuracy, even when power feeding from the power transmissionside to the power reception side is not performed. Therefore, thenon-contact power transmission system is not limited to the magneticfield resonance type, and is applicable to an electromagnetic inductiontype with an increased coupling factor k and a lower quality factor.

Moreover, a power receiver may have a power transmission section andtransmit power to a power transmitter through a secondary-side coilwithout contact. Alternatively, a power transmitter may have a load andreceive power from a power receiver through a power transmission coilwithout contact.

Note that in the above-described first to third embodiments, a qualityfactor at a resonance frequency is measured. However, a frequency atwhich a quality factor is measured may not correspond to a resonancefrequency. Even when a quality factor is measured with use of afrequency which is shifted within a tolerable range from a resonancefrequency, detection accuracy of a foreign metal existing between apower transmission side and a power reception side may be improved byapplying the technology of the disclosure.

Furthermore, approach of a conductor such as a metal to a primary-sidecoil or a secondary-side coil causes change not only in a quality factorbut also in an L value, thereby shifting a resonance frequency. Anelectromagnetic coupling state may be detected with use of a shiftamount of the resonance frequency due to the change of the L value,together with a quality factor.

In addition, a coupling factor k also changes when a foreign metal issandwiched between a primary-side coil and a secondary-side coil. Theelectromagnetic coupling state may be detected with use of such changein the coupling factor k, together with the change in the qualityfactor.

Moreover, in the first to third embodiments of the disclosure, althoughan example of a coil which does not have a core is described as aprimary-side coil and a secondary-side coil, a coil wound around a corehaving a magnetic body in a structure may be employed.

Furthermore, in the first to third embodiments of the disclosure, anexample where a mobile phone is used as a mobile device on a secondaryside is described. However, the mobile device on the secondary side isnot limited thereto, and various mobile devices necessitating power suchas a mobile music player and a digital still camera are applicable.

A series of processes according to the embodiment described above may beexecuted by hardware or software. When being executed by software, theseries of processes is executed by a computer which incorporatesprograms configuring the software in a dedicated hardware, or a computerhaving installed programs for executing various kinds of functions. Forexample, programs configuring desired software may be executed by ageneral-purpose personal computer by installation.

Moreover, a recording medium in which program codes of softwareimplementing the functions of the embodiments may be provided to asystem or a device. It is needless to say that the functions areachievable by allowing a computer (or a control device such as a CPU) inthe system or the device to read out and execute the program codesstored in the recording medium.

Examples of the recording medium providing the program codes in thiscase include a flexible disc, a hard disk, an optical disc, amagneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a non-volatilememory card, and a ROM.

Moreover, the program codes read out by the computer is executed toachieve the functions of the embodiments. In addition, based oninstructions of the program codes, OS or the like operating on thecomputer performs a part or all of the actual processing. The case wherethe functions of the above-described embodiments are achieved by theprocessing is also acceptable.

Furthermore, in the specification, process steps describing processes intime series include processes performed in time series along a describedorder, and also processes which is not necessarily performed in timeseries but is performed in parallel or individually (for example,parallel processes or processes by objects).

It is to be understood that the disclosure is not limited to theabove-described embodiments, and other various modifications andapplication examples may be made.

In other words, the examples of the above-described embodiments arepreferred specific examples of the disclosure, and therefore variouslimitations suitable in technology may be attached. However, thetechnical scope of the disclosure is not limited to these embodimentsunless otherwise specified in each description. For example, the usedmaterials and used amount, the processing time, the processing order,the numerical conditions of the parameters, and the like described inthe above description are merely preferred examples, and the dimensions,the shapes, and the positional relationships in the figure used fordescription are also given schematically.

Note that the present disclosure may be configured as follows.

(1) An energy receiver including:

a power receiver coil configured to wirelessly receive power transmittedfrom a power transmitter;

a detection section configured to detect a foreign object; and

a power storage section configured to supply power to the detectionsection during detection of the foreign object.

(2) The energy receiver of (1), further including:

a Q-value detection circuit connected to the power receiver coil,

wherein the detection section is configured to measure a quality factorrelated to the Q-value detection circuit.

(3) The energy receiver of (1), further including:

a control section configured to activate the detection section duringsuspension of power transmission to the power receiver coil using powerstored in the power storage section.

(4) The energy receiver of (3), wherein the control section includes anarithmetic processing section and a determination section, thearithmetic processing section configured to (i) calculate a qualityfactor related to the power receiver coil, and (ii) output the qualityfactor to the determination section, the determination sectionconfigured to compare the quality factor with a threshold value fordetermining whether the foreign object is within a range of the powerreceiver coil.

(5) The energy receiver of (4), further including:

a memory configured to store the threshold value for determining whetherthe foreign object is within the range of the power receiver coil,

wherein,

-   -   the memory is non-volatile memory in communication with the        control section, and    -   the threshold value is obtained when the power receiver coil is        substantially isolated from the foreign object.

(6) The energy receiver of (1), further including:

a switch in communication with the power storage section, the switchconfigured to (i) connect the power storage section and the detectionsection to provide power for detection of the foreign object duringsuspension of power transmission, and (ii) disconnect the power storagesection and the detection section when the foreign object is not beingdetected.

(7) A detection method including:

charging a power storage section using power wirelessly received from apower receiver coil;

detecting whether a foreign object is within a range of the powerreceiver coil using a detection section; and

powering the detection section during detection of the foreign objectusing the power storage section.

(8) The detection method of (7), further including:

activating the detection section during suspension of power transmissionto the power receiver coil using power stored in the power storagesection.

(9) The detection method of (7), wherein,

the power receiver coil includes a Q-value detection circuit, and

the detecting whether the foreign object is within the range of thepower receiver coil is based on a measurement by the detection sectionof a quality factor related to the Q-value detection circuit.

(10) The detection method of (9), wherein the charging of the powersection includes receiving power wirelessly from a power transmitterbased on power consumed during measurement of the quality factor.

(11) The detection method of (8), further including:

obtaining a threshold value for determining whether the foreign objectis within the range of the receiver coil when the power receiver coil isisolated from the foreign object;

storing the threshold value in a non-volatile memory in communicationwith a control section;

calculating a quality factor using an arithmetic processing section ofthe control section; and

comparing the quality factor with the threshold value using adetermination section of the control section.

(12) The detection method of (7), wherein the powering of the detectionsection includes (i) connecting the detection section to the powerstorage section using a switch so that power is provided to the powerstorage section during suspension of power transmission for detection ofthe foreign object, and (ii) disconnecting the power storage section andthe detection section when the foreign object is not being detected.

(13) A power transmission system including:

a power transmitter configured to wirelessly transmit power to a powerreceiver,

wherein,

-   -   the power transmitter includes (i) a power transmission coil        configured to transmit power to the power receiver, (ii) a power        transmission section configured to supply an AC signal to the        power transmission coil, and (iii) a power transmitter control        section configured to control the supply of the AC signal from        the power transmission section in response to a signal        transmitted from the power receiver, and    -   the power receiver includes (i) a power receiver coil configured        to wirelessly receive power from the power transmitter, (ii) a        detection section configured to detect a foreign object, (iii) a        power storage section configured to store the power received        from the power transmitter, the power storage section operable        to supply the power received to the detection section during        detection of the foreign object, and (iv) a power receiver        control section configured to operate the detection section and        determine whether the foreign object is within a range of the        power transmission coil.

(14) The power transmission system of (13), wherein,

the power receiver includes a Q-value detection circuit connected to thepower receiver coil, and

the detection section is configured to measure a quality factor relatedto the Q-value detection circuit.

(15) The power transmission system of (13), wherein the power receivercontrol section is configured to activate the detection section duringsuspension of power transmission between the power transmitter and thepower receiver using power stored in the power storage section.

(16) The system of (13), wherein,

the power receiver includes a memory configured to store a thresholdvalue for determining whether the foreign object is between the powertransmission coil and the power receiver coil, and

the memory is non-volatile memory in communication with the powerreceiver control section.

(17) The system of (13), wherein the power receiver includes a switch incommunication with the power storage section, the switch configured to(i) connect the power storage section and the detection section toprovide power during suspension of power transmission between the powertransmitter and the power receiver during activation of the detectionsection, and (ii) disconnect the power storage section and the detectionsection when the detection section is not activated.

(18) A detection device including:

a power receiver coil configured to wirelessly receive power transmittedfrom a power transmitter;

a detection section configured to detect whether a foreign object iswithin a range of the power receiver coil; and

a power storage section configured to supply power to the detectionsection during detection of the foreign object.

(19) The detection device of (18), wherein,

the power receiver coil includes a Q-value detection circuit, and

the detection section is configured to measure a quality factor relatedto the Q-value detection circuit.

(20) The detection device of (18), further including:

a control section configured to activate the detection section duringsuspension of power transmission to the power receiver coil using powerstored in the power storage section.

(21) The detection device of (19), further including:

a memory configured to store a threshold value obtained when the powerreceiver coil is isolated from the foreign object; and

a control section in communication with the memory, the control sectionconfigured to (i) calculate the quality factor using an arithmeticprocessing section of the control section, and (ii) compare the qualityfactor with the threshold value using a determination section of thecontrol section.

(22) The detection method of (18), further including:

a switch configured to (i) connect the power storage and the detectionsection to provide power during suspension of power transmission to thepower receiver coil during activation of the detection section, and (ii)disconnect the power storage section and the detection section when thedetection section is not activated.

(23) An energy transmitter including:

a power transmission coil configured to wirelessly transmit power to apower receiver;

a detection section configured to detect a foreign object; and

a power storage section configured to supply power to the detectionsection during detection of the foreign object.

(24) The energy transmitter of (23), wherein the detection section isconfigured to measure a quality factor to determine whether the foreignobject is within a range of the power transmission coil.

(25) The energy transmitter of (23), further including:

a control section configured to activate the detection section duringsuspension of power transmission from the power transmission coil usingpower stored in the power storage section.

(26) The energy transmitter of (24), further including:

a memory configured to store a threshold value for determining whetherthe foreign object is within the range of the power transmission coil,

wherein,

-   -   the memory is non-volatile memory in communication with the        control section, and    -   the threshold value is obtained when the power transmission coil        is substantially isolated from the foreign object.

(27) The energy transmitter of (23), further including:

a switch in communication with the power storage section, the switchconfigured to (i) connect the power storage section and the detectionsection to provide power during suspension of power transmission fromthe power transmission coil when the detection section is activated, and(ii) disconnect the power storage section and the detection section whenthe detection section is not activated.

(28) An energy receiver including:

a power receiver coil configured to wirelessly receive power transmittedfrom a power transmitter;

a detection section configured to detect a foreign object; and

a control section configured to activate the detection section duringsuspension of power transmission to the power receiver coil.

(29) The energy receiver of (28), further including:

a power storage section configured to supply power to the detectionsection during detection of the foreign object.

(30) The energy receiver of (28), further including:

a Q-value detection circuit connected to the power receiver coil,

wherein the detection section is configured to measure a quality factorrelated to the Q-value detection circuit.

(31) The energy receiver of (28), wherein the control section includesan arithmetic processing section and a determination section, thearithmetic processing section configured to (i) calculate a qualityfactor related to the power receiver coil, and (ii) output the qualityfactor to the determination section, the determination sectionconfigured to compare the quality factor with a threshold value fordetermining whether the foreign object is within a range of the powerreceiver coil.

(32) The energy receiver of (28), further including:

a memory configured to store the threshold value for determining whetherthe foreign object is within the range of the power receiver coil,

wherein,

-   -   the memory is non-volatile memory in communication with the        control section, and    -   the threshold value is obtained when the power receiver coil is        substantially isolated from the foreign object.

(33) The energy receiver of (29) further including:

a switch in communication with the power storage section, the switchconfigured to (i) connect the power storage section and the detectionsection to provide power for detection of the foreign object duringsuspension of power transmission, and (ii) disconnect the power storagesection and the detection section when the foreign object is not beingdetected.

(A) A detector including:

a resonance circuit including a secondary-side coil;

a detection section measuring a quality factor of the resonance circuit;

a power storage section charging power, from power received through thesecondary-side coil from a primary-side coil, by an amount of powerconsumed during the quality factor measurement in the detection section;and

a control section operating the detection section, during suspension ofpower transmission from the primary-side coil, with use of the powercharged in the power storage section.

(B) The detector according to (A), wherein the control section operatesthe detection section to measure the quality factor of the resonancecircuit, and detects an electromagnetic coupling state between thesecondary-side coil and the outside.

(C) The detector according to (B), further including:

a first switch section switching supply and suspension of the power tothe power storage section, the power being received from theprimary-side coil;

a second switch section provided between the power storage section and aload, and switching connection and disconnection between the powerstorage section and the load; and

a third switch section switching connection and disconnection betweenthe resonance circuit and the detection section, wherein

the control section switches the first switch section to supply thepower from the secondary-side coil to the power storage section, andthus charges the power storage section, and

after charging the power, in the power storage section, by an amount ofpower consumed during the quality factor measurement in the detectionsection, during the suspension of the power transmission from theprimary-side coil, the control section switches the second switchsection to disconnect the power storage section from the load, switchesthe third switch section to connect the resonance circuit and thedetection section, and operates the detection section with use of thepower charged in the power storage section to measure the quality factorof the resonance circuit.

(D) The detector according to (C), wherein the control sectiondetermines whether the current quality factor measurement is a firsttime measurement, and when the quality factor measurement is determinedas the first time measurement, the control section allows the detectionsection to measure quality factors for measurement signals of aplurality of frequencies, compares a threshold with a maximum qualityfactor of the measured quality factors, and detects an electromagneticcoupling state between the secondary-side coil and the outside, based onthe comparison result.

(E) The detector according to (D), wherein when it is determined thatthe current quality factor measurement is a second or later measurement,the control section allows the detection section to measure a qualityfactor with use of a measurement signal of a frequency at which themaximum quality factor is obtained in the previous quality factormeasurement, compares the threshold and the quality factor measured atthis time, and detects an electromagnetic coupling state between thesecondary-side coil and the outside, based on the comparison result.

(F) The detector according to (E), wherein the control section comparesthe quality factor obtained in the second or latter quality factormeasurement with the maximum quality factor obtained in the previousquality factor measurement to determine whether the quality factormeasured at this time is within a predetermined range of the previousmeasured quality factor, and when the quality factor is not within thepredetermined range, the control section allows the detection section tomeasure quality factors for measurement signals of a plurality offrequencies, compares the threshold with the maximum quality factor ofthe measured quality factors, and detects an electromagnetic couplingstate between the secondary-side coil and the outside, based on thecomparison result.

(G) The detector according to any one of (C) to (F), wherein

the power is charged in the power storage section by an amount of powerenabling the detection section to measure a quality factor with use of ameasurement signal of one frequency, and

the control section controls switching of the first switch section, thesecond switch section, and the third switch section to repeat the chargeand the quality factor measurement alternately.

(H) The detector according to any one of (A) to (G), wherein the powerstorage section is a capacitor or a small secondary battery.

(I) A power receiver including:

a secondary-side coil;

a resonance circuit including the secondary-side coil;

a detection section measuring a quality factor of the resonance circuit;

a power storage section charging power, from power received through thesecondary-side coil from a primary-side coil, by an amount of powerconsumed during the quality factor measurement in the detection section;and

a control section operating the detection section, during suspension ofpower transmission from the primary-side coil, with use of the powercharged in the power storage section.

(J) A power transmitter including:

a primary-side coil transmitting power to a secondary-side coil;

a power transmission section supplying an AC signal to the primary-sidecoil; and

a control section controlling the supply of the AC signal from the powertransmission section in response to a signal indicating anelectromagnetic coupling state based on a quality factor of a powerreceiver, the signal being transmitted from the power receiver mountedwith the secondary-side coil.

(K) A non-contact power transmission system including:

a power transmitter transmitting power by wireless; and

a power receiver receiving the power transmitted from the powertransmitter,

wherein

the power receiver includes:

-   -   a resonance circuit including a secondary-side coil;    -   a detection section measuring a quality factor of the resonance        circuit;    -   a power storage section charging power, from power received        through the secondary-side coil from a primary-side coil, by an        amount of power consumed during the quality factor measurement        in the detection section; and    -   a first control section operating the detection section, during        suspension of power transmission from the primary-side coil,        with use of the power charged in the power storage section, and

the power transmitter includes:

-   -   the primary-side coil transmitting power to the secondary-side        coil of the power receiver;    -   a power transmission section supplying an AC signal to the        primary-side coil; and    -   a second control section controlling the supply of the AC signal        from the power transmission section in response to a signal        indicating an electromagnetic coupling state based on a quality        factor of the power receiver, the signal being transmitted from        the power receiver.

(L) A detection method including:

charging power, in a power storage section of a power receiver in anon-contact power transmission system, by an amount of power consumedduring quality factor measurement in a detection section of the powerreceiver, from power received from a primary-side coil of a powertransmitter through a secondary-side coil of a resonance circuit, theresonance circuit being provided in the power receiver;

operating the detection section and acquiring a physical amountnecessary for determining a quality factor of the resonance circuit,during suspension of power transmission from the primary-side coil, withuse of the power charged in the power storage section; and

calculating the quality factor from the physical amount necessary fordetermining the quality factor, by the power receiver or the powertransmitter in the non-contact power transmission system.

As used herein, the terms “energy receiver” and “power receiver” may beused interchangeably. The terms “power transmission system” and“non-contact power transmission system” may be used interchangeably. Theterms “detection device” and “detector” may be used interchangeably. Theterms “energy transmitter” and “power transmitter” may be usedinterchangeably.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2011-149465 filed in theJapan Patent Office on Jul. 5, 2011, the entire content of which ishereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed:
 1. An energy receiver comprising: a power receiver coilconfigured to wirelessly receive power transmitted from a powertransmitter; a detection section configured to detect a foreign object;and a power storage section configured to supply power to the detectionsection during detection of the foreign object.
 2. The energy receiverof claim 1, further comprising: a Q-value detection circuit connected tothe power receiver coil, wherein the detection section is configured tomeasure a quality factor related to the Q-value detection circuit. 3.The energy receiver of claim 1, further comprising: a control sectionconfigured to activate the detection section during suspension of powertransmission to the power receiver coil using power stored in the powerstorage section.
 4. The energy receiver of claim 3, wherein the controlsection includes an arithmetic processing section and a determinationsection, the arithmetic processing section configured to (i) calculate aquality factor related to the power receiver coil, and (ii) output thequality factor to the determination section, the determination sectionconfigured to compare the quality factor with a threshold value fordetermining whether the foreign object is within a range of the powerreceiver coil.
 5. The energy receiver of claim 4, further comprising: amemory configured to store the threshold value for determining whetherthe foreign object is within the range of the power receiver coil,wherein, the memory is non-volatile memory in communication with thecontrol section, and the threshold value is obtained when the powerreceiver coil is substantially isolated from the foreign object.
 6. Theenergy receiver of claim 1, further comprising: a switch incommunication with the power storage section, the switch configured to(i) connect the power storage section and the detection section toprovide power for detection of the foreign object during suspension ofpower transmission, and (ii) disconnect the power storage section andthe detection section when the foreign object is not being detected. 7.A detection method comprising: charging a power storage section usingpower wirelessly received from a power receiver coil; detecting whethera foreign object is within a range of the power receiver coil using adetection section; and powering the detection section during detectionof the foreign object using the power storage section.
 8. The detectionmethod of claim 7, further comprising: activating the detection sectionduring suspension of power transmission to the power receiver coil usingpower stored in the power storage section.
 9. The detection method ofclaim 7, wherein, the power receiver coil includes a Q-value detectioncircuit, and the detecting whether the foreign object is within therange of the power receiver coil is based on a measurement by thedetection section of a quality factor related to the Q-value detectioncircuit.
 10. The detection method of claim 9, wherein the charging ofthe power section includes receiving power wirelessly from a powertransmitter based on power consumed during measurement of the qualityfactor.
 11. The detection method of claim 8, further comprising:obtaining a threshold value for determining whether the foreign objectis within the range of the receiver coil when the power receiver coil isisolated from the foreign object; storing the threshold value in anon-volatile memory in communication with a control section; calculatinga quality factor using an arithmetic processing section of the controlsection; and comparing the quality factor with the threshold value usinga determination section of the control section.
 12. The detection methodof claim 7, wherein the powering of the detection section includes (i)connecting the detection section to the power storage section using aswitch so that power is provided to the power storage section duringsuspension of power transmission for detection of the foreign object,and (ii) disconnecting the power storage section and the detectionsection when the foreign object is not being detected.
 13. A powertransmission system comprising: a power transmitter configured towirelessly transmit power to a power receiver, wherein, the powertransmitter includes (i) a power transmission coil configured totransmit power to the power receiver, (ii) a power transmission sectionconfigured to supply an AC signal to the power transmission coil, and(iii) a power transmitter control section configured to control thesupply of the AC signal from the power transmission section in responseto a signal transmitted from the power receiver, and the power receiverincludes (i) a power receiver coil configured to wirelessly receivepower from the power transmitter, (ii) a detection section configured todetect a foreign object, (iii) a power storage section configured tostore the power received from the power transmitter, the power storagesection operable to supply the power received to the detection sectionduring detection of the foreign object, and (iv) a power receivercontrol section configured to operate the detection section anddetermine whether the foreign object is within a range of the powertransmission coil.
 14. The power transmission system of claim 13,wherein, the power receiver includes a Q-value detection circuitconnected to the power receiver coil, and the detection section isconfigured to measure a quality factor related to the Q-value detectioncircuit.
 15. The power transmission system of claim 13, wherein thepower receiver control section is configured to activate the detectionsection during suspension of power transmission between the powertransmitter and the power receiver using power stored in the powerstorage section.
 16. The system of claim 13, wherein, the power receiverincludes a memory configured to store a threshold value for determiningwhether the foreign object is between the power transmission coil andthe power receiver coil, and the memory is non-volatile memory incommunication with the power receiver control section.
 17. The system ofclaim 13, wherein the power receiver includes a switch in communicationwith the power storage section, the switch configured to (i) connect thepower storage section and the detection section to provide power duringsuspension of power transmission between the power transmitter and thepower receiver during activation of the detection section, and (ii)disconnect the power storage section and the detection section when thedetection section is not activated.
 18. A detection device comprising: apower receiver coil configured to wirelessly receive power transmittedfrom a power transmitter; a detection section configured to detectwhether a foreign object is within a range of the power receiver coil;and a power storage section configured to supply power to the detectionsection during detection of the foreign object.
 19. The detection deviceof claim 18, wherein, the power receiver coil includes a Q-valuedetection circuit, and the detection section is configured to measure aquality factor related to the Q-value detection circuit.
 20. Thedetection device of claim 18, further comprising: a control sectionconfigured to activate the detection section during suspension of powertransmission to the power receiver coil using power stored in the powerstorage section.
 21. The detection device of claim 19, furthercomprising: a memory configured to store a threshold value obtained whenthe power receiver coil is isolated from the foreign object; and acontrol section in communication with the memory, the control sectionconfigured to (i) calculate the quality factor using an arithmeticprocessing section of the control section, and (ii) compare the qualityfactor with the threshold value using a determination section of thecontrol section.
 22. The detection method of claim 18, furthercomprising: a switch configured to (i) connect the power storage and thedetection section to provide power during suspension of powertransmission to the power receiver coil during activation of thedetection section, and (ii) disconnect the power storage section and thedetection section when the detection section is not activated.
 23. Anenergy transmitter comprising: a power transmission coil configured towirelessly transmit power to a power receiver; a detection sectionconfigured to detect a foreign object; and a power storage sectionconfigured to supply power to the detection section during detection ofthe foreign object.
 24. The energy transmitter of claim 23, wherein thedetection section is configured to measure a quality factor to determinewhether the foreign object is within a range of the power transmissioncoil.
 25. The energy transmitter of claim 23, further comprising: acontrol section configured to activate the detection section duringsuspension of power transmission from the power transmission coil usingpower stored in the power storage section.
 26. The energy transmitter ofclaim 24, further comprising: a memory configured to store a thresholdvalue for determining whether the foreign object is within the range ofthe power transmission coil, wherein, the memory is non-volatile memoryin communication with the control section, and the threshold value isobtained when the power transmission coil is substantially isolated fromthe foreign object.
 27. The energy transmitter of claim 23, furthercomprising: a switch in communication with the power storage section,the switch configured to (i) connect the power storage section and thedetection section to provide power during suspension of powertransmission from the power transmission coil when the detection sectionis activated, and (ii) disconnect the power storage section and thedetection section when the detection section is not activated.
 28. Anenergy receiver comprising: a power receiver coil configured towirelessly receive power transmitted from a power transmitter; adetection section configured to detect a foreign object; and a controlsection configured to activate the detection section during suspensionof power transmission to the power receiver coil.
 29. The energyreceiver of claim 28, further comprising: a power storage sectionconfigured to supply power to the detection section during detection ofthe foreign object.
 30. The energy receiver of claim 28, furthercomprising: a Q-value detection circuit connected to the power receivercoil, wherein the detection section is configured to measure a qualityfactor related to the Q-value detection circuit.
 31. The energy receiverof claim 28, wherein the control section includes an arithmeticprocessing section and a determination section, the arithmeticprocessing section configured to (i) calculate a quality factor relatedto the power receiver coil, and (ii) output the quality factor to thedetermination section, the determination section configured to comparethe quality factor with a threshold value for determining whether theforeign object is within a range of the power receiver coil.
 32. Theenergy receiver of claim 28, further comprising: a memory configured tostore the threshold value for determining whether the foreign object iswithin the range of the power receiver coil, wherein, the memory isnon-volatile memory in communication with the control section, and thethreshold value is obtained when the power receiver coil issubstantially isolated from the foreign object.
 33. The energy receiverof claim 29 further comprising: a switch in communication with the powerstorage section, the switch configured to (i) connect the power storagesection and the detection section to provide power for detection of theforeign object during suspension of power transmission, and (ii)disconnect the power storage section and the detection section when theforeign object is not being detected.